The invention relates to a pneumatically actuatable disc brake having a caliper straddling a brake disc, brake pads which are able to be pressed against the brake disc on both sides, wherein one of the brake pads on a brake application side is able to be actuated by use of a brake lever of a brake application device which may be pivoted about an eccentric axis and against which a brake ram bears on the front face.
Such a pneumatically actuatable disc brake is disclosed, for example, in EP 0 553 105 B1 and EP 1 230 491 B1.
In this connection, the brake lever which is formed at one end as an eccentric is supported on the brake caliper as an abutment. Due to the relatively large pivot angle of the brake lever, required by its operation, correspondingly high friction losses of the eccentric bearing arrangement are present. For the reduction of these friction losses, therefore, rolling bearing half-shells are used which enclose the eccentric bearing arrangement.
However, the production of such rolling bearings is only possible by a very complex manufacturing process, with correspondingly high production costs.
In addition, such a rolling bearing arrangement is naturally relatively susceptible to failure, which hinders an optimized service life.
It is proposed, therefore, in the aforementioned EP 1 230 491 B1, to use plain bearings exclusively for mounting the brake lever on the caliper. The plain bearings are characterized by a particularly high degree of robustness, in addition to low production costs. However, the coefficients of friction of the maintenance-free plain bearings used are many times above the roll resistance value of the rolling bearings, which naturally has an effect on the provision of a braking force to be applied by the brake cylinder.
For optimizing the pneumatically actuated disc brake, therefore, it is proposed in DE 10 2008 004 806, which is not pre-published, to provide the disc brake with a self-energizing device, which has a self-energizing factor selected so that the brake is automatically released after braking.
By this measure, the stroke of a brake cylinder, by which the brake lever may be actuated by an attached plunger, may be substantially shorter, naturally resulting in a reduction of the pivot angle of the brake lever, due to the reduction of the coefficient of friction of the pivot bearing.
Thus, a pressure ram is attached to the brake lever, the pressure ram moving in the axial direction of the brake disc when the brake lever is rotated and pressing the brake pad attached on the brake application side against the brake disc.
For supporting the brake pad and for producing the self-energizing device, viewed in the peripheral direction of the brake disc, a pressure ram is arranged in each case on both sides of the brake ram. The pressure rams are mounted, on the one hand, on the caliper and, on the other hand, corresponding to the brake pad. Moreover, the pressure rams, in cooperation with a wear adjusting device, serve to compensate for clearance as a result of wear.
In EP 1 230 491 B1 discussed above, for producing the plain bearing arrangement of the brake lever in the caliper, spherical cap-shaped bearing receptacles are provided, in which bearing elements in the form of balls engage which, on the other hand, are supported on the brake lever.
For machining the bearing receptacles it is necessary to form the caliper in two parts and to screw the two halves of the caliper together after machining. This screw connection, however, represents a potential weak point as the screws have to absorb the forces acting on the caliper.
The introduction of through-bores and threaded bores, and the provision of the screws themselves, represent a factor which has a negative effect on production costs, which is of particular importance, in particular with regard to the fact that disc brakes are mass-produced items which are used in large numbers.
The object of the invention, therefore, is to develop a disc brake of the above-described type so that it may be produced more easily and more cost-effectively, and so that its operational reliability is permanently improved.
This and other objects are achieved by a disc brake having a caliper straddling a brake disc, brake pads which are able to be pressed against the brake disc on both sides, wherein one of the brake pads on a brake application side is able to be actuated by use of a brake lever of a brake application device which may be pivoted about an eccentric axis and against which a brake ram bears on the front face. The brake ram, on the other hand, is coupled to the brake pad on the brake application side or a guide plate connected thereto. Two pressure rams are aligned with the brake ram and arranged at a distance therefrom, which in each case are attached to the caliper and coupled to the brake pad or the guide plate. A self-energizing device is also provided. The caliper includes spherical cap-shaped bearing receptacles, in which plain bearing elements adapted thereto engage, via which the brake lever and the pressure rams are supported on the caliper at a side remote from the brake pad.
With this structural design, the spherical cap-shaped bearing receptacles may be dimensioned to be so small that a suitable machining tool may be introduced into a one-piece caliper design.
Thus the machining tools, generally machining spindles, have to be guided obliquely relative to the rotational axis of the brake disc. In order to keep the corresponding angle still within additional limits in the sense of accurate machining, the caliper back is expediently designed so that a sufficient free passage is provided for the machining spindle without loss of strength.
By the spherical cap-shaped design of the bearing receptacles, when using a suitable tool a substantially free angular position of the rotational axis of the machining spindle may be selected. Above all, therefore, this is particularly advantageous as concentric guidance of the machining spindle is not possible through the caliper back, as otherwise the caliper back would be reduced in its strength in an unacceptable manner by the corresponding through-holes.
The self-energizing device which encompasses a guide plate, to which the brake pad is fastened, as well as a wedge system, requires a larger sized shaft of the brake, relative to a disc brake without self-energization, which promotes the insertion of the machining tool into the interior of the caliper.
Instead of an obliquely guided machining spindle, the spherical cap-shaped bearing receptacles may also be machined by driven angular milling heads, so that a coaxial machining of the bearing receptacles is possible.
Although, as mentioned above, the size of the shaft of the brake caliper is increased by the use of the self-energizing device, the overall space requirement of the disc brake, viewed in the direction of the brake disc axis, is reduced by the now reduced stroke of the brake cylinder and the reduced pivot angle of the brake lever.
According to an advantageous development of the invention, the pressure ram(s), the brake ram and the wear adjustment device, including a synchronization device for the synchronous adjustment of the wear, together with a base plate abrading the mounting opening of the caliper and the guide plate, are combined to form a structural unit.
The pressure ram is coupled to the brake pad so that small pivoting movements of the pressure ram are possible, corresponding to the peripheral displacement of the brake pad occurring when the brake is actuated.
Simple releasability of the coupling of the pressure ram to the brake pad, which is required in the event of maintenance, is preferably provided via a snap connection, for example in the form of a spring washer received in a groove of the brake ram, which at high tensile forces, as are required for releasing the connection when changing the pad, is forced back from an annular oblique shoulder on the brake pad completely into the groove, so that the two components, the brake ram/brake pad, are separated.
Instead of being provided in the pressure ram, the groove for receiving the spring washer may also be provided on the brake pad, in particular a pad carrier plate of the brake pad, whilst the annular oblique shoulder is provided on the associated component.
The return force required for releasing this connection is considerably greater, preferably many times greater, than the spring force of the return spring in order to prevent the connection from being inadvertently released.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.